Spotter.....
A divergent phugoid is a way of assessing the long period longitudinal instability of an aircraft. The aircraft is set up and trimmed in straight and level flight and the control column is pushed / pulled to upset the pitch stability of the aircraft. The length of time taken to recover to straight and level flight (and the number of pitch oscillations) is a measure of the stability of the aircraft and the graph of the pitch characteristics of the aircraft describes a phugoid. A divergent phugoid is one where there is negative stability and the amplitude of the pitch oscillations increases.
The closest equivalent analogy I can think of is the shock absorbers on your car - if you depress one corner of the car, the correct response (assuming good shock absorbers) is a decaying sinusoidal pitch oscillation.
Another similie is a Tank slapper on a bike!
Good luck with the course, but dont tell anyone you're going!
